German patent document No. 2,919,105 filed by R. Verbickas et al with a claim to the priority of U.S. application Ser. No. 907,502 filed May 19, 1978, now abandoned and U.S. Pat. Nos. 2,776,586 and 3,857,268 describe the use of working rolls of noncylindrical shape in a roll stand, and the provision of means for displacing at least one of these rolls axially relative to the other and for bending at least one of these rolls. In this manner it is possible to change the dimension of the gap or so-called nip formed between the two rolls.
The bending equipment for the roll adds considerably to the cost of the rolling stand. On the one hand it is necessary to provide roll-bending devices that bend the ends of the roll away from the nip, so-called positive bending, and separate equipment for bending of the ends of the roll toward the nip, so-called negative bending. Positive bending increases the pressure at the longitudinal edges of a workpiece being rolled and negative bending decreases this pressure, for corresponding decreases and increases in workpiece thickness at these edges.
It is possible to achieve only minimal variations in nip dimensions without this bending equipment. That is, without using the bending equipment it is impossible to achieve anything other than slight variations in a workpiece with longitudinal edges thicker than its middle.
Not only is this type of arrangement quite expensive, but accurately establishing the proper amount of bend in conjunction with the right axial position of the working roll is very difficult, requiring expert setup personnel and frequent monitoring during operation to verify that the system remains properly set up. What is more, when positive bending is employed it is necessary to exert enormous forces against the working-roll ends, so that the roll-stand housing must be overdimensioned considerably.
In the copending application cross referred to above a roll stand is described having a conventional housing defining a pair of parallel and spaced axes defining a plane. Respective rolls have roll ends journaled in the housing at the axes and roll bodies axially symmetrical about the respective axes and having centered on the respective axes complementary roll-body surfaces of noncylindrical shape and each formed by rotation of a continuously curved generatrix about the respective axis. One of these contoured rolls is displaceable axially relative to the other roll from an end position to another position, and the roll-body surfaces form at the plane in the other position a uniform nip and in the end position a nonuniform nip. Finally the system has means for displacing one of the rolls axially relative to the other of the rolls between the end position and the other position. These contoured rolls may themselves define the nip, or may engage and deform other rolls that define it.
With this arrangement therefore the shape of the roll-body surfaces--wholly contoured with no cylindrical portions--allows the nip to be adjusted solely by axial displacement of one of the rolls relative to the other. In addition the shape of the nip and the corresponding cross section of the workpiece is varied by relatively minor shifting of the contoured roll, with no effect on the overall nip width. Thus the workpiece cross section can be changed without having to readjust for a different workpiece width.
According to a feature of this earlier invention the roll bodies are of identical shape but the one roll is reversed 180.degree. relative to the other roll. This is achieved most advantageously when the surfaces each have one half of outwardly convex shape and another half of outwardly concave shape. In such an arrangement it is possible for the nip to be set to impart to the workpiece a cross section of uniform thickness, of greater thickness at the outer longitudinal edges, or of greater thickness at the center. Regular and stepless variation from the one shape to the other can be easily achieved and will surely remain set in the apparatus. Even a relatively unskilled person can set up the rolling stand according to this invention to achieve the exact shape desired.
The system of this earlier invention works extremely well, but is susceptible of improvement.